The present invention concerns implantable medical devices, such as defibrillators and cardioverters, and more specifically to a method of manufacturing a capacitor for an implantable heart monitor.
Since the early 1980s, thousands of patients prone to irregular and sometimes life-threatening heart rhythms have had miniature heart monitors, particularly defibrillators and cardioverters, implanted in their bodies, typically in the upper chest area above their hearts. These devices detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric current to the heart. When the bursts of electric current are properly sized and timed, they restore normal heart function without human intervention, sparing patients considerable discomfort and often saving their lives.
The typical defibrillator or cardioverter includes a set of electrical leads, which extend from a sealed housing into the wall of a heart after implantation. Within the housing are a battery for supplying power, monitoring circuitry for detecting abnormal heart rhythms, and a capacitor for delivering bursts of electric current through the leads to the heart.
The capacitor can take the form of a flat aluminum electrolytic capacitor. Flat capacitors include a stack of flat capacitor elements mounted within a capacitor case. Each flat capacitor element includes one or more separators between two sheets of aluminum foil. One of the aluminum foils serves as a cathode (negative) foil, and the other serves as an anode (positive) foil. Sometimes, two or more foils are stacked one on the other to form a multi-anode stack. The capacitor elements each have an individual capacitance (or energy-storage capacity) proportional to the surface area of the aluminum foil.
One drawback with these capacitors is that they consume significant space within the implantable defibrillators and cardioverters and thus limit how small these devices can be made. However, the size of the capacitor cannot be arbitrarily reduced without reducing the capacitance of the device. Accordingly, there is a need to reduce the size of the capacitor while also maintaining or increasing its capacitance. Further, there is a need to provide a compact capacitor capable of providing the required pulse of energy for use within the device and to provide for a design efficiently utilizing space within the capacitor case.
In one aspect, the present invention provides a capacitor having an active case. In one embodiment, the active case comprises a cathodic case. In another embodiment, the active case comprises an anodic case.
One aspect provides a capacitor having an active cathodic case which services an adjacent anode. In one embodiment, a capacitor includes a case having an etched inner surface, the inner surface including an etched upper inner surface and an etched lower inner surface. The capacitor further includes a capacitor stack disposed within the case, where the capacitor stack includes a plurality of cathode stacks and a plurality of anode stacks, and the cathode stacks are electrically coupled with the etched inner surface. The plurality of anode stacks include a first anode stack disposed adjacent to the upper inner surface, where the first anode stack includes at least one conductive layer having a major surface. The major surface confronts the upper inner surface of the case. The capacitor further includes electrolyte disposed between the upper inner surface and the major surface to facilitate charge storage between the inner surface and the major surface.
In one embodiment, a method includes forming and aligning a capacitor stack including at least one anode stack and at least one cathode stack, etching at least a portion of an inner surface of a capacitor case, the inner surface including an upper inner surface and a lower inner surface. The method further includes disposing the capacitor stack in the capacitor case, and at least one anode stack is adjacent the inner surface of the capacitor case. The method also includes disposing an electrolyte between the at least one anode and the inner surface of the case.
One aspect provides a capacitor having an active anodic case. In one embodiment a capacitor assembly includes at least one anode stack having one or more anode conductive layers and an anode separator, and at least one cathode stack having one or more cathode conductive layers and a cathode separator. The capacitor assembly further includes at least one separator disposed between the anode stack and the cathode stack, where each at least one anode stack stacked with the cathode stack to form a capacitor stack, and a capacitor case sized to receive therein the capacitor stack. The capacitor case includes a conductive surface therein, and one or more of the anode conductive layers is electrically coupled with the conductive surface of the capacitor case.
In one embodiment, the capacitor case comprises an etched capacitor case. In another embodiment, the assembly includes a cathode feedthrough coupled with at least one cathode stack, where the cathode feedthrough extends through and is insulated from an opening of the case. In yet another embodiment, one or more of the anode conductor layers includes an exposed edge coupled with the capacitor case. In one embodiment, each of the cathode conductive layers is defined in part by a cathode edge surface, and each of the anode conductive layers is defined in part by an anode edge surface, where the cathode edge surface is offset from the anode edge surface. The assembly optionally further includes a welded connection disposed between at least one of the one or more anode conductive layers and an inner surface of the case. The assembly optionally further includes a conductive epoxied connection disposed between at least one of the one or more anode conductive layers and an inner surface of the case.
Among other advantages, in one or more embodiments, an active anodic case contributes to the effective anodic surface area which increases the capacitance of the capacitor without increasing the outer packaging dimensions. Alternatively, it allows for achievement of a given total capacitance with a smaller package. An active cathodic case provides that an outer cathode layer is not needed on the capacitor stack to service the anodes. This decreases the size of the capacitor. A further benefit is that since the edge of the cathode stack is offset from the anode stack, damage or puncturing of the separator layer is minimized.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following is description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims and their equivalents.